The present invention relates to epoxy resins suitable for use in coating and adhesive formulations and processes for making the same. In particular, the present invention relates to epoxy resin compositions capable of faster cure at low temperature.
Epoxy resin compositions suitable for use in coating and adhesive formulations are well known. They are commercially available as the one-component type and the two-component type. The two-component type comprises a polyepoxide composition and a hardener. The polyepoxide composition cures after the hardener is admixed with the polyepoxide composition. The two-component type is often used when a particularly durable, corrosion-resistant, and strongly adherent coating or seal is required for large metal or concrete structures such as bridges, ships, industrial tanks, etc., where application of the coating or seal must be performed under ambient conditions.
A problem often associated with two-component type epoxy coatings is that the rate of cure is significantly reduced at low temperatures, especially at temperatures below 10° C. and particularly at temperatures below 5° C. At such low temperatures, many epoxy curing agents also tend to rise to the surface during cure, which tends to leave a greasy film on the surface. The greasy film tends to have an adverse effect on the appearance of the coating or seal and can lead to intercoat adhesion failure when subsequent coating or sealing layers are applied.
One approach currently used to address this problem is to use phenalkamine hardeners in combination with difunctional epoxy resins based on bisphenol A in winter grade epoxy formulations. While this approach is capable of curing at low ambient temperatures to provide coatings resistant to corrosion having a good appearance, the rate of cure remains slower than desired by coatings and sealants users.
It has been observed that when the functionality of the epoxy resin is increased to try to accelerate the cure rate, coatings made by combining such higher functional epoxy resins with phenalkamine hardeners have a grainy appearance and form a nonhomogeneous film that remains sticky for a long period of time.
A two-component type polyepoxide composition and hardener combination is therefore desired that provides a nonsticky epoxy coating or seal having a good appearance and high resistance to corrosion at a faster low ambient temperature cure rate.
The present invention solves this and other problems as described in more detail below.